Characteristics of the liquid flame spray process

Liquid flame spraying (LFS) is a new thermal spray process. Liquid feedstock is injected and atomized in an oxygen-hydrogen flame where the liquid phase is evaporated and thermochemical reactions are completed to produce fine particles. Production of nanoparticles requires a thorough understanding of the process. Therefore, various process stages were studied; i.e., the atomization of Liquid feedstock, and characterization of the flame and flame-droplet interactions. Experimental techniques included laser diffraction anemometry for droplet size distribution, laser doppler velocimetry for particle velocity, pulsed laser Rayleigh back scattering for flame temperature and Schlieren photography for flame structure. Atomization is optimized with an organic solvent, such as isopropanol, nebulized with hydrogen gas at a high flow rate. Liquid droplets injected into the flame are subjected to a maximum temperature of 2600 degrees C and are accelerated to about 160 m s(-1), The flame length call be controlled by flame velocity and the solvent type. Water produces a shorter name whereas isopropanol extends the flame. Injection of the aerosol produces a ''pencil-like'' region which does not experience turbulence for most of the flame length. Experimentation with manganese nitrate and aluminium isopropoxide or aluminium nitrate showed conversion to a manganese oxide and alumina, respectively. (C) 1997 Elsevier Science S.A.